Preventing rusting of steel sheets coated with aqueous slurry of metal powder

ABSTRACT

IN COATING STEEL SHEET WITH AQUEOUS SLURRY OF METAL POWDER, THE SLURRY IS ADDED WITH CORROSION INHIBITOR TO PREVENT RUSTING OF STEEL SHEET AT THE TIME OF DRYING THE COATING LAYER THEREBY IMPROVING ADHESION THEREOF TO THE STEEL SURFACE, SAID CORROSION INHIBITOR ADDITING BEING A COMPOUND CONTAINING ANY ONE OF SUCH NEGATIVE IONS AS NO2-,MOO4--ORC6H5COO- IN A CONCENTRATION RANGING FROM 10**-5 MOL/L. TO 10**-1 MOL/L.

Sept. 12, 1972 H YAMAGISHI ETAL 3,690,940

PREVENTING RUSTING OF STEEL SHEETS COATED WITH AQUEOUS SLURRY OF METALPOWDER Filed NOV. 1'7, 1970 MM 8 M my 6 L U\v SE55 mmim 20 who; 53 6 ozION CONCENTRATION (MOLAR) United States Patent Int. Cl. B22f 7/04; C23c17/00 US. Cl. 117-131 2 Claims ABSTRACT OF THE DISCLOSURE In coatingsteel sheet with aqueous slurry of metal powder, the slurry is addedwith corrosion inhibitor to prevent rusting of steel sheet at the timeof drying the coating layer thereby improving the adhesion thereof tothe steel surface, said corrosion inhibitor addition being a compoundcontaining any one of such negative ions as N0 MoO or C H COO- in aconcentration ranging from mol/l. to 10- mol/l.

The present invention relates to a metal coating method for steelsheets, and more particularly to a method of improving on the adhesionof metal coating layer to the surface of the steel sheet by restrainingrusting of the steel sheet which is coated with metal powder inaccordance with the water-slurry method at the stage of drying saidmetal coating layer.

As for the method of coating surface of steel sheets with a slurry whichis prepared by admixing metal powder and a solution, there are one ortwo methods known in the prior art. However, there is yet no establishedtechnique relating to the use of corrosion inhibitor as an additive tosuppress the rusting of steel sheet. Therefore, the adhesion of coatinglayers and steel sheets is always reduced in any of the conventionalmethods as the steel surface starts rusting at the stage of dryingsubsequent to coating. And it has been the common practice to useorganic solvents in lieu of water in order to obviate such drawbacks.This is still defective in that it may very well lead to generation ofpoisonous gas and danger of fire as well as it is expensive, althoughthe use of organic solvent may help restrain the rusting.

Under the afore-mentioned circumstances, the present invention has beendeveloped to provide a novel and useful method in improving on theadhesion of a metal coating layer by modifying thejconventionalwater-slurry coating method in adding a corrosion inhibitor instead oforganic solvent so as to prevent rusting of steel sheet. Moreparticularly, it comprises coating steel sheet with a slurry of metalpowder, drying, rolling and heat-treating the same. Said slurry containsone or more of the compounds which contain any one of such negative ionsas N0 1 MoO.;-, C H COO in a concentration ranging from 10- mol/l. to 10mol/l.

Reference is now made to the accompanying drawing in which the curvesshow the effect of the corrosion inhibitors employed in the presentinvention. Very small amount of said corrosion inhibitors is added tothe waterslurry of metal powder in coating the same on steel sheet. Asthe curves indicate, the amount to be added may vary in accordance withthe types of inhibitors used, but is within the range of from 10- mol/l.to 10- mol/l. It is desirable that the corrosion inhibitor is a compoundcontaining any one of such negative ions as N0 Mo0 and C H COO, which issoluble in water and which would not chemically react with the particlesof metal powder.

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As is evidently understood from the drawing, the concentration of theinhibitor to be added is specified as in the range from l0 mol/l. to 10-mol/l. because:

(1) no efiect thereof can be expected when said concentration is lessthan l0 mol/L, thereby it is determined that 10* mol/l. is the minimumrequired amount; on the other hand,

(2) the addition of the corrosion inhibitor exceeding 10- mol/l. mayimpair the adhesion of coating layer to steel sheet or the finish of thesurface, thereby it is determined that 10- mol/l. is the upper limit ofthe range which will not deteriorate the coating layer.

The addition may be carried out by adding any one or more of thecorrosion inhibitors into water to dissolve therein, to which metalpowder is introduced to prepare a slurry.

Application of coating is not restricted to any particular method normeans, and can be done in accordance with the generally practiced wayssuch as curtain-flow method, spray method or methods using bar-coaters,roll-coaters or brushes.

After being coated with a slurry, the steel sheet will be heated to suchan extent as to dry the coating layer or to have the metal particlessinter slightly. It is then subjected to rolling in order to improve onthe adhesion of the coating layer to the steel sheet. The coating layerafter the rolling should show hardening due to the workings, and thus itbecomes inferior in the drawability. By removing the warping due to theworkings under such heattreatment conditions as inhibit the formation ofalloyed layer between the coating layer and the steel sheet, metalcoated steel sheet having excellent adhesion and Workability may beobtained.

In case drawing is necessary, it is desirable to conduct temper rollingafter the heat-treatment.

EXAMPLE 1 Slurry containing 1,500 g. of aluminum powder, 10- mol/l. ofNaNO and 1,000 g. of water is coated on steel sheet with a reverseroll-coater to have the coating layer after drying weigh 80 g./m. Afterdrying the coating layer, the steel sheet is rolled to elongate by 7%,and then subjected to heat-treatment in an oxidizing atmosphere of 600C. for 2 minutes.

The resultant product has a gloss surface and is superior inanti-corrosiveness and workability.

EXAMPLE 2 Slurry containing 1,500 g. of aluminum powder, 10 mol/l. of NaMoO and 1,200 g. of Water is applied on a steel sheet with the use of abar-coater.

The amount of coating is g./m. when weighed after drying. The steelsheet thus coated is then subjected to heat-treatment in an oxidizingatmosphere for 30 seconds in a furnace temperature of 650 C. and torolling to elongate by 5%. It is further treated for post-agingtreatment in an electric furnace the temperature of which is maintainedat 400 C. and rolled for temper regulation.

The resultant product is of the same properties as that of Example 1,and exhibits anti-corrosiveness for more than 1,200 hours when subjectedto salt spray test (JIS Z2371).

EXAMPLE 3 Slurry containing 1,500 g. of aluminum powder, 10- mol/l. of CH COONa, l0- mol/l. of Na MoO and 1,000 g. of water is applied on steelsheet with the use of sprayer. It is subjected to succeeding proceduresidentical to those of Example 1 such as drying and rolling. The amountof coating weighed after drying is 75 g./m. The ratio of elongation atthe time of rolling is 5%. The heattreatment is conducted in accordancewith the induction heating system which is so controlled as to raise thetemperature of the steel surface to 500 C., in two minutes.

The resultant product is of the same properties as those of Examples 1and 2. It is superior in anti-corrosiveness, and peeling-01f of thecoating layer is not observed when formed into sash .(window frame).

As can be understood from the foregoing description, the presentinvention enables the improvement of the adhesion of coated layer tosteel sheet since the rusting or corrosion at the time of drying issuppressed in steel sheet coated with water-soluble paint andwater-slurry. The employment of water in lieu of organic solvent as thedispersing agent in the present invention is economically advantageous.The present invention eliminates danger of fire as compared with theconventional method, as well as it is harmless to bodies. Thus, numerousadvantages can be expected of the present invention. Also, it may wellbe applicable to all the corrosion preventive methods in the fieldwherein a coating is formed on steel sheet with the use of water as amedium such using water-soluble paint, water-slurry, water-solubleemulsion or the like.

What is claimed is:

1. In the method of applying a metal coating layer on a steel sheetwherein a steel sheet is contacted with a slurry of a metal powder andwater following by drying, rolling to improve adhesion of the coatinglayer to the steel sheet and heat-treating to improve workabilitythereof, the improvement which comprises so contacting said steel sheetwith an aqueous slurry of metal powder containing a water-solublecompound containing an ion selected from the group consisting of N0 MoOand 4 C H COO in a concentration of from about 10- mol/l. to about 10-mol/l.

2. In the method of applying a metal coating layer on a steel sheetwherein a steel sheet is contacted with a slurry of a metal powder andwater following by drying, rollling and heat-treating, the improvementwhich comprises so contacting said steel sheet with an aqueous slurry ofmetal powder containing an ion selected from the group consisting of N0M005" and C H COO-, in a concentration of from about 10- mol/l. to about10" mol/l.

References Cited UNITED STATES PATENTS DeHart 1466.l4 RX ALFRED L.LEAVITI, Primary Examiner J. R. BATTEN, JR., Assistant Examiner US. Cl.X.R.

Patent No.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3, 690,940 DatedSeptember 12,1972

H'. YAMAGISHI et al Inventor(s) It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 4 Claim 2 should be rewritten as follows:

"The method of Claim 1, wherein the metal powder is aluminum powder."

Signed and sealed this 16th day of April l97h.

(SEAL) Attesb:

" MARSHALL DANN EDWARD I-I.I"LETCHER,JR. v.

Commissioner of Patents Attes'bing Officer- UScOMM-DC 60376-P69 w u.s.GOVERNMENT mmnm; orrlc: "l9 o-up-au.

F ORM PO-105O (10-69) UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent 690,940 Dated September 12,1972- H; YAMAGISHI et alInventor(s) o It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 4 Claim 2 should be rewritten as follows:

"The method of Claim 1, wherein the metal powder is aluminum powder."

Signed and sealed this 16th, day of April 19%..

(SEAL) Attest:

EDT-{ARI I TJ LETCHEILJR. C. MARSHALL DANN Attestinp; OfficerCommissioner of Patents FORM PO-1050 (10-69) uscoMM-Dc 60376-P69 1 Hi5.GOVERNMENT PRINTING OFHFE "l9 0-!!6-334,

